The present invention relates to devices for allowing homogeneously blending two or more liquid components into a uniform composition. More particularly, the invention relates to the mixing and blending of liquid coating materials, wherein the materials may be formed of two or more components which are initially segregated, and are mixed into a uniform consistency at or near the point of application. The applicator for coating materials of the general type is typically a spray gun or other similar device, and the delivery vehicle for providing coating materials to the applicator is typically a reciprocable pumping system.
There are a great many liquids which find useful purpose in industry, and which are formed by proportioning and mixing several different liquid components prior to application. Included among such liquids are various types of paints, sealants and adhesives, each of which are typically stored in component containers, and the plural components are proportioned and mixed during the application process. Liquid pumping equipment may be connected to the individual component containers, and the pumping equipment may be controlled so as to withdraw a predetermined ratio of components from the respective containers for delivery over a single liquid delivery line. Static mixing manifolds are typically placed into the liquid delivery line flow path so as to cause turbulence in the flow of the respective liquids and thereby to efficiently mix the plural components into a homogeneous liquid for delivery to the applicator. Industrial plants frequently utilize reciprocable pumps which draw from the respective component containers, wherein the pumps are jointly linked and driven by a single reciprocable motor so as to withdraw the liquid components from the respective containers in a uniform ratio. The proper ratio may be selected by appropriately selecting the delivery capacity of the pumps, by controlling the respective reciprocation strokes of the pumps, or by other liquid metering devices The liquid components are subsequently conveyed along a single supply line to an applicator, although one or more mixing devices are typically inserted into the delivery line to ensure proper mixing of the proportioned liquids.
The present invention does not relate to the aforementioned mixing devices, including static mixing manifolds and other similar devices, which are primarily used to cause turbulence in the liquid flow path so as to insure thorough mixing of liquid components. Mixers of this general type will homogeneously mix liquid components, but have no capability for redistributing liquid components which may flow through the delivery lines in improper mix ratios; i.e., a static mixer will cause turbulence to thereby mix a liquid composite at a point in space along the delivery line, in whatever mix ratio the liquid composite is formed of at that mixing point.
A particular problem arises from the use of pumps, particularly reciprocable stroke pumps, which problems are evidenced during transitions from starting, stopping and stroke reversal. The volume of liquid delivered by a pump upon initial startup, or upon shutdown, can vary the optimal mix ratio of the plural components being delivered. Similarly, when a reciprocable pump changes its stroke direction, it typically causes a sudden pressure drop and pressure surge which results in a transient liquid delivery condition. These liquid transients cause the delivery system to vary from its uniform volume delivery characteristics, and when two or more reciprocable pumps are interconnected in a plural component delivery system, the respective liquid transients may occur at different instants in time. This results in liquid volumes having component ratios which are uniformly consistent in the liquid delivery lines, but interspersed by liquid volumes which may be improperly ratioed, resulting from the transient delivery conditions described above. When visualized in a liquid delivery line such activity results in a uniform flow of mixed liquid components which are properly ratioed, interspersed by intermittent "slugs" of improperly ratioed mixed components. The use of static mixers in a liquid delivery line will thoroughly mix the components moving through the lines, but will not correct component ratios which are outside of desired parameters. By and large, the plural component liquids tend to move through the delivery lines in uniformly mixed volumes, but without correcting for volume segments which may be improperly ratioed. Ratioing problems require a different form of blending of liquid volumes as the liquid passes through the delivery lines.